1. Field of the Invention
The present invention relates to a power circuit switch and more particularly particular relates to a power circuit switch whose performance is improved by altering the grease that is applied to the sliding part constituting the power circuit switch and the sliding conduction part.
2. Description of the Related Art
In high-voltage, high-current power circuits, compared with low-voltage, low-current power circuits, the physical impact and/or resistance caused by contact/separation of the contacts on switching the power circuit are considerable. Consequently, a power circuit switch for switching high-voltage/high-current power circuits is typically provided with a high-voltage charging unit equipped with a vacuum valve (vacuum interrupter) for actually performing the switching of the power circuit and an operating mechanism for mechanically operating this vacuum valve.
A vacuum valve is provided with a pair of contacts (electrodes); switching of the power circuit that is connected thereto is effected by contacting/separating these contacts. The operating mechanism performs a mechanical reciprocating action on the contacts in order to effect contact/separation of the contacts. Such an operating mechanism comprises a sliding member such as a bearing for effecting reciprocating action; grease that gives lubrication is applied to the sliding member in order to maintain a smooth action and to prevent frictional wear.
Also, the power circuit switch is provided with a conductive part for effecting electrical connection with the main circuit; in this conducting part also, a sliding action is performed in effecting contact/separation of the conductor of the power circuit switch and the conductor of the main circuit. Grease is applied to such portions also.
As the conventional grease which is used for such sliding portions, typically, grease is employed containing a urea thickener, with a mineral oil base.
However, with the conventional grease, due to solidification or thickening (a deterioration of the sliding condition) caused by deterioration over a period of years, the short-time operating performance is adversely affected and there is a possibility of the sliding member becoming inoperable; periodic maintenance of the grease has therefore been considered necessary.
Also, in power circuit switches, the sliding member may be left under elevated-temperature conditions due to the generation of heat by the high voltage and high current. In such cases, the conventional grease was liable to deteriorate due to poor durability under elevated-temperature conditions. This therefore led to the drawback that, in sliding parts of the conducting part etc., contact resistance of the conductor was increased due to solidification of the grease, resulting in increased local heating, causing the power loss to become large.
Accordingly one object of the present invention is to provide a novel power circuit switch of excellent long-term reliability by reducing the power loss by suppressing the contact resistance of the conducting parts to a low level and improving operating reliability of the power circuit switch over a long period, by using a grease of improved performance in respect of deterioration over a period of years in a power circuit switch.
In order to achieve the above object, a power circuit switch according to the present invention comprises an operating mechanism that drives contact/separation of contacts, and a sliding conduction part that forms electrical contacting of these contacts and a main circuit on receiving a contact pressure, grease being applied to the mechanical sliding part of the operating mechanism and to the sliding conduction part, wherein the grease has as base oil at least one synthetic oil whose kinematic viscosity is 30-500 mm2/s at 40xc2x0 C. and is selected from the group consisting of poly xcex1-olefins, poly xcex1-olefin hydrides and dialkyl diphenyl ethers, and contains as thickener 5-30 mass % of a urea compound.